Organic Chemistry 2 Lab Final

What is the stationary phase in TLC?

Silica gel

is silica gel polar or nonpolar

very polar

What does the moblie phase do in TLC?

carries the compounds up the plate

what does a low Rf value indicate?

the compound is polar and sticks to silica

what does a high Rf value indicate?

the compound is nonpolar and moves far with the solvent

three uses of TLC?

track reaction progress, check purity, identify unknowns

how do you caluclate Rf?

distance spot traveled / distance solvent front traveled

what is the main purpose of the wittig-horner reactions?

convert aldehydes into alkenes

What reagent forms the ylide in wittig-horner reaction

sodium methoxide (base)

what carbonyl compounds is used in the wittig-horner reaction?

cinnamaldehyde

what is the product of your wittig-horner reaction?

E,E-1,4-diphenyl-1,3-butadiene

what is the electrophile in electrophilic aromatic substitution (nitration)

nitronium in (NO2+)

how is NO2+ formed?

by mixing concentrated HNO3 and H2SO4

What type of director is methyl benzoate? (nitration)

meta-directing (due to strong EWG)

why must the nitration reaction be kept cold?

to avoid forming di-nitrated products

in electrophilic aromatic substituent reaction, what determines where the electrophile attaches?

the substituent already on the benzene ring

what two components react in a diels-alder reaction?

a diene and a dienophile

what type of mechanism is the diels-alder reaction?

concerted (no intermediates)

which product is favored: endo or exo?

endo (due to secondary orbital interactions)

in diels-alder reaction, how is 1,3-butadiene generated in your experiment?

by heating butadiene sulfone

what is the sterochemical rule for diels-alder?

stereochemistry of the dienophile is perserved

what forms the enolate in the aldol reaction

acetone + NaOH

why cant benzaldehyde form an enolate?

It has no α-hydrogens

What is the intermediate formed before dehydration in aldol condensation reaction?

β-hydroxy ketone

What is the final product of aldol condensation reaction?

Dibenzylacetone (a conjugated α,β-unsaturated ketone).

Why does the aldol condensation reaction happen twice?

Acetone has α-hydrogens on both sides

what is the product of cyclohexanol oxidation?

cyclohexanone

what is the oxidizing agent used? (oxidation of cyclohexanol)

bleach (sodium hypochlorite, NaOCl)

why must bleach be added slowly? (oxidation of cyclohexanol)

the reaction is exothermic (heats up quickly)

how do you test for leftover hypochlorite? (oxidation of cyclohexanol)

starch-iodine paper (turns blue if hypochorite remains)

what technique is used to isolate cyclohexanone?

steam distillation

what reagent is used to form the epoxide? (expodation of trans-stilbene)

mCPBA

what happens to the sterochemistry during epoxidation?

it is perseved (trans-alkene → trans-epoxide)

what technique monitors reaction progress?

TLC every 15-60 minutes

what is the purpose of washing with NaHCO3?

neutralizes leftover mCPBA and acid

what does solubitlity in water with pH < 7 indicate?

carboxylic acid

what does solubility in HCl indicate?

amine (forms ammonium salt)

what does bubbling with NaHCO3 mean?

carboxylic acid reacting to form CO2

what does DNPH test confirm?

presence of aldehyde or ketone

what does tollens’ test indicate?

aldehyde (forms silver mirror)

where does an aldehyde proton appear in H NMR?

9-10ppm

where does a carboxylic acid proton appear?

11-12ppm

what is the IR peak for a carbonyl

1700cm-1

why must TLC lines be drawn in pencil?

ink runs with solvent; pencil does not

what happens if the solvent level touches your sample spots during development?

the samples dissolve into the solvent → ruined plate

what is a co-spot and why is it used?

spot of both starting material + product; helps confirm identity when Rf values are similar

why do spots appear larger or streaky sometimes?

the sample was too concentrated

why do we mark the solvent front immediately?

because the solvent evaporates quickly; you lose the Rf measurement

what type of intermediate forms before alkene formation? (wittig-horner)

oxaphosphetane

what drives the wittig-horner reaction to completion?

formation of a stable phosphonate oxide byproduct

what type of bond is created in the wittig-horner product?

a new carbon-carbon double bond

why is the product usually (E)-alkene in the wittig-horner reaction?

because stabilized ylides favor trans products

what role does H2SO4 play in forming NO2+? (aromatic substitution)

acts as a strong proton donor (acid) to generate NO2+ from HNO3

what is the rate-determining step of Electrophilic aromatic substitution?

forming the sigma-complex (arenium ion)

why is methyl benzoate deactiviting? (electrophilic aromatic substitution)

the carbonyl withdraws electron density from the ring

what functional group appears in the product’s IR spectrum after nitration?

NO2 symmertric and asymmetric stretches (1350-1530cm-1)

what must the diene be in for the Diels-alder reaction to occur

s-cis conformation

in diels-alder reaction, what gas is released when forming butadiene from butadience sulfone?

SO2 gas

what sterochemistry is preserved in the dienophile?

cis or trans configuration is directly passed into the product

why is the endo product favored?

extra orbital overlap (secondary interactions)

what type of reaction is Aldol: addition, elimination, or both?

both (addition → dehydration)

In aldol condensation reaction what happens in the dehydration step?

loss of water to form a conjugated double bond

what indicates the completion of aldol condenstation?

formation of yellow/orange crystals

In aldol condensation reaction, what is the driving force for the final product?

conjugation (increase stability)

In oxidation of cyclohexanol reaction, what color does starch-iodine paper turn in presence of hypochlorite?

dark blue/black

in oxidation of cyclohexanol reaction, what destroys extra bleach before distillation?

sodium bisulfite (NaHSO3)

what is the key IR peak for cyclohexanone?

ketone stretch at 1715cm-1

what technique removes water from organic layers?

using a drying agent like MgSO4

why add boiling stones during distillation?

prevent violent boiling (bumping)

in epoxidation of stilbene reaction, what type of mechanism does peracid epoxidation follow?

concerted (no intermediates)

what functional group is produced in the product IR? (epoxidation of stilbene)

epoxide C-O stretch (1200cm-1)

what does a successful TLC for epoxidation show after 1 hr?

starting material spot disappears

what does insoluble in water, soluble in NaOH indicate?

phenol or carboxylic acid

what does insoluble in water, soluble in HCl indicate?

amine

what is the appearance of a positive DNPH test?

yellow/orange/red solid

what is a positive Tollens’ test result?

silver mirror

what NMR region represents aromatic protons?

7-8ppm

what IR peak indicates an alcohol (non-acidic)?

broad peak around 3300cm-1

what IR peak indicates a carboxylic acid OH?

very broad peak from 2500-3300cm-1

what is the derivative used for identifying aldehydes/ketones by melting point?

DNPH, semicarbazone, or oxime

what is the purpose of refluxing?

heat reaction without losing solvent

what piece of equipment is used for vacuum filtration?

buchner funnel

what is the purpose of recrystallization?

purify solid products

what happens if crystals fail to form?

strach glass with stirring rode

what is percent yield formula

(actual yield / theoretical yield) x 100

why record melting point range?

identify purity and confirm product identity

what is the mechanism type of the diels-alde reaction?

a pericyclic, concerted [4+2] cycloaddition

First step of aldol?

Base removes a-H → enolate forms.

First step of nitration?

H2SO4 protonates HNO3 → NO2+

first steps of epoxidation?

peracid transfers an oxygen atom to alkene

first step of wittig-horner?

base deprotonates phosphonate → ylide forms

strong sharp 1700 cm-1

carbonyl

very broad 2500-3000cm-1

carboxylic acid OH

medium peaks around 2700 & 2800 cm-1

aldehyde C-H

peaks at 1250cm-1

epoxide C-O stretch

two strong peaks around 1350 and 1530cm-1?

nitro group

9-10ppm

aldehyde proton

11-12ppm

carboxlyic acid proton

7-8ppm

aromatic protons

5-6ppm

alkene protons